How is polyethylene made from ethylene?

Polyethylene is produced through the polymerization of ethylene (CH₂=CH₂), a gaseous hydrocarbon. During this process, the double bond between the carbon atoms is broken, allowing the molecules to link together into long, repeating chains.1

The specific method of production determines the type of polyethylene created:

• Low-Density Polyethylene (LDPE): Produced under very high pressures and temperatures using oxide initiators. This results in a polymer structure with both long and short branches, creating a flexible material.1
• High-Density Polyethylene (HDPE): Manufactured at low temperatures and pressures using Ziegler-Natta catalysts or activated chromium oxide. The lack of branches allows the chains to pack closely, resulting in a dense, strong material.12
• Linear Low-Density Polyethylene (LLDPE): Created by copolymerizing ethylene with other monomers (such as 1-butene) using Ziegler-Natta or metallocene catalysts. This produces a linear backbone with short, uniform branches.12

These catalytic processes, particularly the use of organometallic compounds, revolutionized the industry by allowing polymerization to occur at significantly lower pressures and temperatures than earlier methods.32